William Newman originally announced SBCL as a variant of CMUCL in December 1999.[2] The main point of divergence at the time was a clean bootstrapping procedure: CMUCL requires an already compiled executable binary of itself in order to compile the CMUCL source code, whereas SBCL supported bootstrapping from - theoretically - any ANSI-compliant Common Lisp implementation.

SBCL became a SourceForge.net project in its own right in late 2000. The original rationale for the fork was to continue the initial work done by Newman without destabilizing CMUCL which was at the time already a mature and much used implementation. The forking was amicable, and there has since then been significant flows of code and other cross-pollination between the two projects.

Since then SBCL has attracted several developers, been ported to multiple hardware architectures and operating systems,[3] and undergone many changes and enhancements: while it has dropped support for several CMUCL extensions that it considers beyond the scope of the project (such as the Motif interface) it has also developed many new ones, including native threading and Unicode support.

Version 1.0 was released in November 2006, and active development continues. As of 2011, the documentation is quite substantial but still considered a work in progress[4] by the developers.

William Newman stepped down as project administrator for SBCL in April 2008.[5] Several other developers have taken over interim management of releases for the time being.[6]